package html

import "strings"

// path.go: ParseBlockID extracts the slot sequence from a data-block ID.
// Example: ParseBlockID("L-0-C-0") returns []byte{'L', 'C'}.
func ParseBlockID(id string) []byte {
	if id == "" {
		return nil
	}

	// Split on "-" and require the exact structural pattern:
	// slot, numeric index, slot, numeric index, ...
	var slots []byte
	i := 0
	for part := range strings.SplitSeq(id, "-") {
		if i%2 == 0 {
			if len(part) != 1 {
				return nil
			}
			if _, ok := slotRegistry[part[0]]; !ok {
				return nil
			}
			slots = append(slots, part[0])
		} else {
			if part == "" {
				return nil
			}
			for j := range len(part) {
				if part[j] < '0' || part[j] > '9' {
					return nil
				}
			}
		}
		i++
	}
	if i == 0 || i%2 != 0 {
		return nil
	}
	return slots
}